Large social phenomena could come a few days / years / months sooner or later, they could have different leaders, different victims, somewhat different endings, etc. (It may be good to bet on possibility of slave rebellion in −70s, but becoming friends with Spartacus may be useless.)
Some events (volcanoes, large social phenomena etc) would not be ruled out by butterfly effect, so they’re not strictly cheating.
Vulcanoes, sun eclipses, et cetera are fair game.
Large social phenomena could come a few days / years / months sooner or later, they could have different leaders, different victims, somewhat different endings, etc. (It may be good to bet on possibility of slave rebellion in −70s, but becoming friends with Spartacus may be useless.)